8900 AAVSO

8900 AAVSO, provisional designation 1995 UD₂, is a stony asteroid from the inner regions of the asteroid belt, about 5 kilometers in diameter. It was discovered by American amateur astronomer Dennis di Cicco at the U.S Sudbury Observatory (817), Massachusetts, on 24 October 1995.

The stony S-type asteroid orbits the Sun at a distance of 2.2–2.9 AU once every 4.04 years (1,476 days). Its orbit shows an eccentricity of 0.15 and an inclination of 9 degrees from the plane of the ecliptic.

In 2014, a photometric light-curve analysis at the U.S. Palomar Transient Factory, California, gave it a rotation period of 7000383680000000000♠3.8368±0.0005 hours with a brightness amplitude of 0.43 in magnitude, while the Collaborative Asteroid Lightcurve Link (CALL) assumes an albedo of 0.20, which is a typical value for S-class asteroids.

The minor planet was named after one of the premier astronomical organizations, the American Association of Variable Star Observers (AAVSO). It was founded in 1911 by amateur astronomer William Tyler Olcott (1873–1936), following Harvard astronomer Edward Charles Pickering's (1846–1919) prescient vision of a collaboration between amateurs and professionals in the name of science (also see 784 Pickeringia). The AAVSO is an astronomical pro-am organization that promotes the study of variable stars to both amateur and professional astronomers, maintaining the largest database of variable star observations in the world.

Rho1 Arae

Rho¹ Arae is the Bayer designation for a star in the southern constellation of Ara. Unusually for a star with a Bayer designation, it was not catalogued by Bayer in his Uranometria. It was instead first catalogued by Nicolas Lacaille, in his Coelum Australe Stelliferum published in 1763. This star gained the Bayer designation of Rho¹ Arae in Bode's Uranographia, published in 1801. Rho¹ Arae is one of the dimmest stars with a Bayer designation, having an apparent visual magnitude of just +6.275 According to the Bortle Dark-Sky Scale, this means the star is just barely visible to the naked eye in dark rural skies. Based upon parallax measurements, it is about 640 light-years (200 parsecs) distant from the Sun, give or take a 50 light-year margin of error.

This is a spectroscopic binary system, which means that the presence of an orbiting companion is indicated by shifts in the spectrum. However, because the primary component is spinning rapidly with a projected rotational velocity of 370 ± 10, it is difficult to obtain reliable orbital elements. The orbital period has been estimated at 0.439 days. The spectrum of this system matches a stellar classification of B3 Vnpe, which may indicate the primary is a B-type main sequence star. The 'e' suffix indicates the presence of emission lines, indicating this is a Be star. For Rho¹ Arae, the emission lines are prominent and variable.

R Doradus

R Doradus (HD 29712 or P Doradus) is the name of a red giant Mira variable star in the far-southern constellation Dorado, although visually it appears more closely associated with the constellation Reticulum. Its distance from Earth is 178 ± 10 light-years (54.6 ± 3.1 parsecs). Having a uniform disk diameter of 0.057 ± 0.005 arcsec, it is currently believed to be the star with the second largest apparent size as viewed from Earth (after the Sun). The estimated diameter of R Doradus is 515 ± 70 million km (3.46 AU) or 370 ± 50 times the diameter of the Sun. If placed at the centre of the Solar System, the orbit of Mars and most of the main asteroid belt would be contained within the star.

The visible magnitude of R Doradus varies between 4.8 and 6.6, which makes it usually just visible to the naked eye, but in the infrared it is one of the brightest stars in the sky and its total luminosity is 6500 ± 1400 times that of the Sun. With a near-infrared J band magnitude of −2.6, only Betelgeuse at −2.9 is brighter.